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Does Culling Actually Encourage Poaching Of Endangered Species?

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Conventional wisdom claims that culling is an effective tool for the conservation of endangered predators. But a newly-published study argues that culling may actually encourage poaching of endangered predator species

Wolves are amazing animals. Not only do they inhabit our imaginations -- dressing up as Germanic grannies or bringing bastards back to life -- but they can also trigger all sorts of conniptions in the real world. Historically, they have been a source of conflict with farmers and ranchers, because wolves like to eat the same livestock that we like to eat -- especially when farmers and ranchers over-hunt or displace the wolves' preferred prey.

But recently, the public has become more sympathetic towards wolves. They have as much right as any other animal to inhabit this planet, and they play an important role in our ecosystems. Thus, wolf populations have recently been expanding in both North America and Europe, thanks to conservation efforts. But their increasing numbers are leading to more conflicts with farmers and ranchers, who then want wolves “controlled”.

Authorities in the United States have responded to this controversy by allowing culling of wolves when they endanger people or livestock. In fact, the U.S. Department of Agriculture, the U.S. Fish and Wildlife Service and the Wisconsin Department of Natural Resources argued that the state should be able to implement “lethal and nonlethal” methods to “protect resources from wolf damage and to promote wolf conservation” (ref).

This policy is consistent with conservation practices in Norway, Sweden and Finland, too. Part of this protocol stems from human behavior: if a cull was not allowed, the argument goes, farmers and ranchers would take matters into their own hands, and kill wolves illegally. By allowing legal killing of targeted "problem" individuals, illegal killing of wolves in general is reduced. But does this work in practice?

Today, a study was published in the highly respected journal, Proceedings of the Royal Society of London B, that proposed to test this argument (ref). The two authors, ecologist Guillaume Chapron, Associate Professor at the Grimsö Wildlife Research Station at the Swedish University of Agricultural Sciences, and Adrian Treves, Associate Professor of Environmental Studies at the University of Wisconsin, analyzed data that tracked how wolf population sizes in Wisconsin and Michigan changed between 1995 and 2012 -- a period of time when culling was first banned, then allowed, and then banned again, for a total of 12 times.

The authors developed a mathematical model that related these reported population changes to changes in the legal status of wolf culls, and found that wolf population growth slowed more than expected when culling was legal.

“Each time the state had the authority to cull wolves, we found a decrease in the population growth of wolves”, said Professor Treves in a statement. He also noted that average population growth decreased from 16% to 12% of the annual growth during periods of culling.

But why?

Obviously, the wolves weren't anticipating a cull and leaving the state in droves, nor were their populations so dense that their reproduction rate decreased. Since the authors had eliminated these variables, there was one remaining possibility: the authors attributed this decreased population growth to poaching.

“The political message that government sends when wolves are no longer protected is enough to increase poaching”, argued Professor Treves.

Because their model relies upon a lot of mathematics -- which tends to frighten most people (and even some scientists) -- Professor Chapron created this little video to help explain the study’s methods and implications to the general public:

I really like that video. It's a cute way to explain their findings. But if you actually read the paper itself, you see a different story. Essentially, statistical support for the study's findings is weak to non-existent. I am specifically referring to the large p-value, which, in this case, indicates how certain we can be whether growth or shrinkage of the wolf population is in response to policy changes. In this study, this is the effect that the authors are testing.

"Now, p-values are rightly criticised for a lot of reasons, but what this says is that we cannot be sure of the direction of the effect. This could be because [the effect] is pretty much zero, or because it is difficult to estimate", said biostatistician Robert O'Hara, a senior scientist at the Senckenberg Museum's Biodiversität und Klima Forschungszentrum (BiK-F), who was not part of this study.

How can we distinguish between the two alternatives?

"We can get an idea about this by first noting that the estimated growth rate without any cull is about 0.15, so the population increases by (on average) 16% each year", said Dr O'Hara in an interview.

"So, for example, if there are 500 wolves in one year, in the next there will be (on average) about 580. What is the effect of a cull [that lasts] one year? With the best estimate, the number of wolves would be about 17 fewer (i.e. an increase of 64 wolves rather than 81). But the range is large: the confidence interval suggests it could either be 55 fewer or 24 more wolves. In other words, the population could increase by between 25 or 104 wolves", explained Dr O'Hara.

"This, to me, is a lot of uncertainty", said Dr O'Hara. "Basically, we don’t really know what the effect of culling is."

“Our study uses a Bayesian inference and does not rely on frequentists p-values”, Dr Chapron responded in email.

“The study does not include claims on significance and presents all parameter uncertainties”, said Dr Chapron. “And the fact that culling was 5 times more likely to increase than decrease poaching is a valid and important message.”

Indeed, the presumed value of culling as a conservation practice is an important issue that warrants further study.

"My wish is that this paper will generate more research attention on this topic so that we can learn more and have better evidence based policy", said Dr Chapron.

Source:

Guillaume Chapron and Adrian Treves (2016). Blood does not buy goodwill: allowing culling increases poaching of a large carnivore, Proceedings of the Royal Society of London B, 20152939, published online on 11 May 2016 ahead of print | 10.1098/rspb.2015.2939

Also cited:

USFWS report (2006). Final environmental assessment for the management of wolf conflicts and depredating wolves in Wisconsin.

Does Culling Actually Encourage Poaching Of Endangered Species? | @GrrlScientist

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